Molding is done by injecting plastic material into a mold having at least two parts, which are movable with respect to each other, the moving together of which allows to create the molding cavity, and the moving apart of which allows to eject the molded part. For the axially symmetric containers more specifically envisaged, the mold comprises a female part or matrix having at least one hollow cavity corresponding to the external shape of the container, and a male part or punch having at least one relief cavity corresponding to the internal side of said container.
The invention is applicable to bodies provided with a label sticking to the outer surface of one portion of the wall thereof It sticks thereon due to overmolding performed on the label: the label is introduced into the mold prior to the injection of the plastic material. The label is generally obtained from a plastic film covered with printed patterns. It may also have a multilayer structure comprising a barrier layer against diffusion of gases or flavors, typically of EVOH (ethylene vinyl alcohol), or else of metal, e.g. a PET (polyethylene terephthalate)/aluminum structure. In the latter case, the label preferably covers all or nearly all of the surface of the side wall, i.e. typically more than 95% of said surface.
Usually, before each molding cycle, a label is transferred, e.g. by a claw and/or suction cup system, to the mold, according to several possible techniques. A first technique consists in using a mandrel the shape of which is adapted to penetrate inside the hollow cavity of the matrix. The label is shaped into a cylinder and arranged around the mandrel so as to substantially adapt to the external shape thereof. The label thus deformed is held in touch with the external side of the mandrel by application of at least one holding means, typically applying forces created by a vacuum created inside the mandrel (air suction). When the mandrel arrives inside the cavity of the matrix, the means for holding the label on the mandrel is deactivated, and the label, due to resilience thereof, detaches from the mandrel and makes contact by adapting at least partially to the shape of the side wall of the cavity of the matrix.
Other techniques for placing a label inside the molding cavity have been described. Thus, the patent FR 2 627 744 discloses the use, for transferring labels, of two rotary claws winding up the label like a horn, the label thus wound up being gripped by a transfer claw inserting the label into the matrix of the mold. Furthermore, in the patent EP-B-1 009 610, the label is shaped into a cylinder or truncated cone, and the edges of the label are joined before depositing the same, after shaping thereof, on the punch. Another technique for depositing labels is described in FR 2 656 277, where a device is used comprising a two-part mold carrying a cavity, a label magazine arranged above the mold, a means for supplying a flexible label into the cavity, an organ for gripping the label in the magazine, an organ for depositing the label on a mandrel the outer shape of which corresponds to that of the object to be covered. The depositing organ comprises at least one pair of vertical slides arranged near one of the two lateral flanks of the mandrel, suitable for receiving a label supplied by the gripping organ and positioning the same opposite the mandrel, and at least one jaw having a width smaller than the distance between two slides of the same pair, designed for pushing the vertical flexible label through the pair of slides, then pressing the same against the mandrel flanks.
Furthermore, the patent U.S. Pat. No. 6,616,441 describes a molding device allowing for molded parts to be obtained by vertical injection, using two-part molding tools: a fixed “upper” mold half placed at the output of the injection press, and movable “lower” mold halves placed on an indexed rotary platen operating step by step. When a “lower” mold half is conducted to the molding station, the mold halves are aligned, the molding assembly thus created is closed and then locked, and injection is performed. With respect to “stationary” classical molding devices, this device allows in certain instances for production rates to be increased, but the injection cycle time is still very long because of the difficulties in aligning the mold halves. Also, this document does not provide for the labels to be placed inside the cavities and, if it is envisaged to include such an operation, it can only be done at the injection station, which can only further increase the corresponding cycle time at the injection station. Finally, aligning the tools, balancing the flows of plastic material, and precisely positioning the labels soon turn out to be insurmountable problems if multi-cavity moldings are to be performed, so that it often appears to be more simple and economical to do multi-cavity molding with a stationary classical device rather than a series of single-cavity moldings with a device like the one described in U.S. Pat. No. 6,616,441.